Yukio is slipping. Has been slipping since she came to True Cross in disguise. He was hovering on the edge when she met him years ago. But, Shiro kept it in check then. Until he died and Rin awoke and something happened in Kyoto, and now Yukio’s going down so fast she’s not sure he can stop.

But, she wants to give him the chance.

Because the alternative…

Stop kidding yourself.

The alternative is that Rin’s going to insist on saving something beyond saving, and he’s going to look at her with those eyes, and she’s going to say yes.